The invention relates to a method and an apparatus for processing printing ink containing inhibitors and oligomers in a printing unit of a rotary printing machine.
A printing ink which contains inhibitors and oligomers and is preferably solvent-free and has constituents that can crosslink. While the inhibitors prevent crosslinking of the ink constituents, the inhibitors break down as the result of splitting of the ink into a thin ink film (the principle of ink splitting) and under the action of oxygen in the air.
A disadvantage in the processing of printing ink of this type is that, for specific applications, in particular subsequent processing, the printing ink is not sufficiently dried on the printing material.
It is an object of the present invention to provide a method and apparatus for processing printing ink containing inhibitors and oligomers of the foregoing type in which the ink has shortened drying times and can be used with improved printing quality.
A first advantage of the invention is that the printing ink when applied on the printing material can be dried much faster. As a result, further processing of the printing material can be carried out more efficiently in a rotary printing machine.
A further advantage is that processing of the printing ink can be implemented in a number of the most important printing processes, such as wet offset (using damping solution), dry offset (free of damping solution), letterpress printing, and flexographic printing.
Specifically in offset printing units having damping units (wet offset) or offset printing units for printing free of damping solution (dry offset), it is advantageous to accelerate the drying process for the printing ink by adding a catalyst which accelerates the breakdown of the inhibitors to the damping solution (wet offset) or to the printing ink (dry offset). In this case, it is not necessarily required to introduce the catalyst into all of the offset printing units. Depending on the desired state of drying of the printing ink on the printing material, the catalyst may be added only in selected of the offset printing units. Preferred offset printing units for the addition of catalysts arexe2x80x94as considered in the conveying direction of the printing materialxe2x80x94printing units which are arranged upstream of a sheet turning device and/or a varnishing unit and/or upstream of a sheet deliverer.
Alternatively, in varnishing units operating with a letterpress printing process or a planographic printing process, it is advantageous that the drying of the varnish be accelerated by means of the addition of a catalyst to the varnish that accelerates the breakdown of the inhibitors. Here too, the use of a catalyst is not absolutely necessary in all varnishing units (in the event of a multiple arrangement of varnishing units). Depending on the desired state of drying of the varnish on the printing material, the catalyst can be introduced in selected varnishing units.
Thus, it also is advantageous that the method and apparatus are not restricted to the processing of a printing ink containing inhibitors and oligomers; the process of a varnish containing inhibitors and oligomers can likewise be implemented. The term printing ink, as used herein, therefore also includes such a varnish.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which: